The present invention relates to gas turbine engine fuel injectors and, in particular, fuel injectors for the combustor of a gas turbine engine.
Pressure atomizing fuel injectors for supplying primary fuel and secondary fuel to the combustor of a gas turbine engine are in use. These pressure atomizing injectors typically include a primary fuel tube to provide a relatively low fuel flow rate to a primary fuel discharge orifice of the injector during all regimes of engine operation. The primary fuel tube usually is disposed within a secondary fuel tube that provides a variable, metered secondary fuel flow to a secondary fuel discharge orifice as needed during high power engine operation regimes. During high power engine operation, the secondary fuel flows through the secondary fuel tube about the primary fuel tube to maintain the latter relatively cooler compared to the former.
A particular pressure atomizing fuel injector assembles the primary fuel tube and secondary fuel tube in the injector housing by metallurgical braze or weld joints near opposite ends thereof. During high power engine operation, the fuel injector undergoes thermal expansion and vibration resonance which generate internal stresses, especially on the relatively cooler primary fuel tube, found to cause premature fatigue failure (cracking) of one or more of the brazed joints proximate the opposite ends of the primary fuel tube. Fatigue failure of the braze joints of the primary fuel tube can lead to primary fuel internal leakage and requires costly repair or overhaul of the affected fuel injector.
An object of the present invention is to provide a fuel injector for a gas turbine engine having a fuel tube configured and assembled in an injector housing in a manner to reduce fatigue failure at metallurgical joints positioning the fuel tube in the injector housing and along the length of the fuel tube.
The present invention provides in one embodiment a fuel injector for a gas turbine engine wherein an elongated fuel tube is positioned in an internal passage in a fuel injector housing using metallurgical joints and is provided with a spiral configuration along at least a portion of its length between the joints for engaging an adjacent surface in the housing in line-to-line interference engagement at one or more locations in a manner that reduces fatigue failure (cracking) of the metallurgical joints during service in a gas turbine engine.
In a particular illustrative embodiment of the present invention, a fuel injector includes an elongated primary fuel tube residing within a an elongated secondary fuel tube. The primary fuel tube is positioned by brazed or other metallurgical joints proximate opposite end regions of the primary fuel tube. Between the brazed end regions, the primary fuel tube includes a generally helical spiral configuration or profile that engages the inner wall of the secondary fuel tube in line-to-line interference contact along a sufficient portion of the lengths of the primary and secondary fuel tubes effective to substantially reduce fatigue failure at the brazed joints during engine service. In another illustrative embodiment, the outer secondary fuel tube can include the generally helical spiral configuration, while the primary fuel tube is straight. The spiral of the secondary fuel tube can engage the outer surface of the primary fuel tube and/or the inner surface of a passage in the strut portion of the fuel injector.
The present invention can be practiced with pressure atomizing fuel injectors, airblast fuel injectors, and hybrid airblast-pressure atomizing fuel injectors to this end to reduce fatigue failure of a fuel tube therein.